1. Field of the Invention
The present invention pertains to oral appliances, and, in particular, to oral appliances adapted to prevent partial or complete upper airway obstruction.
2. Description of the Related Art
Obstructive sleep apnea or OSA, obstructive sleep hypopnea, and upper airway resistance syndrome (UARS) are among a variety of known disorders characterized by episodes of complete or partial upper airway obstruction during a state of diminished consciousness, such as sleep, anesthetization, or post anesthesia. OSA, hypopnea, and UARS cause intermittent interruption of ventilation during sleep with the consequence of potentially severe oxyhemoglobin desaturation. Typically, those afflicted with OSA, hypopnea, and UARS experience repeated, frequent arousal from sleep in response to the oxygen deprivation. The arousals result in sleep fragmentation and poor sleep continuity.
Consequences of OSA, hypopnea, and UARS may include debilitating daytime sleepiness and cognitive dysfunction, systemic hypertension, cardiac dysrythmias, pulmonary artery hypertension, and congestive heart failure. Other consequences may include a predisposition to myocardial infarction, angina pectoris, stroke, right ventricular dysfunction with cor pulmonale, carbon dioxide retention during wakefulness as well as during sleep, and continuous, reduced arterial oxygen tension. Moreover, the cognitive impairment resulting from OSA, hypopnea, and UARS puts those afflicted at elevated risk of accidents.
The pathogenesis of the airway obstruction that characterizes OSA, hypopnea, and UARS can include both anatomic and functional abnormalities of the upper airway that result in increased air flow resistance and/or obstruction of air flow. Such abnormalities may include narrowing of the upper airway due to suction forces created during inspiration, the effect of gravity pulling the tongue back to appose the pharyngeal wall, and insufficient muscle tone in the upper airway dilator muscles, among others. It is also believed that excessive soft tissue in the anterior and lateral neck, as commonly observed in obese persons, can apply sufficient pressure to internal structures to narrow the upper airway and restrict air flow.
Conventional treatment of OSA, hypopnea, and UARS has included surgical intervention, such as uvalopalotopharyngoplasty, gastric surgery for obesity, mandibular advancement procedures, maxillo-facial reconstruction, and tracheostomy. However, surgery potentially involves considerable risk of post-operative morbidity and mortality. In addition, the failure rate of surgery is disturbingly high. Pharmacological therapy has also been proposed to treat OSA, hypopnea, and UARS; however, results have been generally disappointing.
Continuous positive airway pressure (CPAP) or bi-level positive airway pressure applied during sleep is commonly used to treat OSA, hypopnea, and UARS patients. Positive pressure is applied to the upper airway to splint or support the airway, thereby preventing its collapse and the resultant airway obstruction. A typical PAP device comprises a flow generator (e.g., a blower) that delivers gas via a delivery conduit to a patient interface. It is also known to deliver the PAP as a continuous positive airway pressure (CPAP), a variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle or an auto-titrating pressure that varies with the monitored condition of the patient. Pressure support therapies are also provided to treat other medical and respiratory disorders, such as Cheynes-Stokes respiration, congestive heart failure, and stroke.
Many patient interfaces are well known in the art. For instance, masks which provide a seal between the compressed air and the patient are common in the art. These interfaces include prongs which fit into the nares of the patient, nasal masks which fit over the patient's nose, and full face masks which fit over the patient's nose and mouth. Although these devices work effectively, they may be uncomfortable for some patients. Moreover, proper fit is often dependent upon the particular user's facial characteristics.
Other patient interfaces have been suggested to deliver positive pressure to a patient that do not depend upon the external facial characteristics of the patient. One such device exemplary of the art is disclosed in U.S. Pat. No. 6,679,257. This device is an oral appliance that is connected to a pressurized gas source, and has a vestibular shield located between the teeth and lips/cheeks of the patient. An oval-shaped tube extends through the shield and into the patient's oral cavity. The oral appliance also includes second shield, or flap, which fits inside the patient's mouth to seal the oral cavity.
Although this device has advanced the art, it also has several drawbacks. For instance, this oral appliance is not securely registered in the patient's mouth. Thus, it could move around and ultimately compromise the seal between the appliance and the patient. Secondly, the device is configured to deliver positive pressure to the patient's airway. As discussed above, positive pressure may be uncomfortable for some patients and interfere with normal breathing.
Another way to retain the patient's airway open is through the use of negative pressure. It has been found that negative pressure may be applied to the patient's oral cavity to draw the patient's soft palate and tongue away from the rear pharyngeal wall. As the soft palate is drawn forward, it seals against the rear portion of the tongue while simultaneously keeping the airway open. U.S. Pat. No. 5,957,133 discloses an oral appliance capable of creating a subatmospheric environment within the patient's mouth. The oral appliance disclosed in this reference has a hollow body with an opening in the rear of the device. The device is connected to a negative pressure vacuum.
Even though this device advances the art, it can be further improved upon. Registration and proper alignment of the device is achieved by dental impressions which must be custom molded in a thermal set material. However, merely opening ones mouth, or yawning during sleep, would be sufficient to undermine this method of registration. Secondly, the appliance provides an opening in the rear of the device to draw the patient's tongue and soft palate away from the posterior pharyngeal wall. However, it does not provide a barrier to prevent other soft tissue, such as the patient's cheeks, from being drawn inward towards the opening and causing discomfort to the user.
Another drawback to this device is that while suction is applied to the device the soft tissue may be drawn towards the opening of the device and partially, or completely, occlude the rear opening of the device. As a result, soft tissue damage can occur due to prolonged suction force. Secondly, while the opening is occluded, the device will be rendered ineffective since it is no longer in fluid communication with the retroglossal area. Yet, another drawback to this device is that it fills a majority of the oral cavity. By reducing the oral volume in the patient's mouth, it impedes anterior movement of the tongue and soft palate to unblock the airway. Accordingly, it would be desirable to have an oral device which is configured to create a negative pressure environment within a patient's oral cavity. It would be further desirable to have an oral appliance that is configured to securely register within a patient's oral cavity. It would also be desirable to have an oral appliance that is configured to prevent soft tissue from being drawn inwardly and causing discomfort to the patient. It would be still further desirable to have an oral appliance that is designed to maximize the available oral volume to enhance comfort and allow the tongue and soft palate to be drawn anteriorly by the applied negative pressure.